In general, ergot alkaloids can be classified according to their different chemical structures, for example ergolines, lysergic acid derivatives, ergot peptide alkaloids and dihydrogenated ergot peptide alkaloids. Clinical applications of ergot alkaloids and their derivatives include treatment of Parkinson's disease, migraine headaches, hyperprolactinemia and cerebro-vascular disturbances, just to name a few.
Many ergot alkaloids and their derivatives are known. For example, U.S. Pat. No. 3,896,228 to Richardson discusses the use of ergot alkaloids to increase urine volume and urine pH. U.S. Pat. No. 3,987,173 to Borredon proposes the use of certain mixtures of vincamine and ergot alkaloids to treat blood circulation disorders. U.S. Pat. No. 4,229,451 to Fehr et al. provides ergopeptine derivatives useful as venoconstrictors and venotonics. U.S. Pat. No. 4,315,937 to Maclay et al. discusses ergots and their use in treating minimal brain dysfunction. U.S. Pat. No. 4,366,145 to Stoopak et al. discusses a soft gelatin capsule with a liquid ergot alkaloid center fill solution. U.S. Pat. No. 4,440,722 to Djorjevic et al. provides a medicine containing salts of ergotamine, ergosinine, ergocryptinine, ergocristinine and ergocominine used for treating arterial hypertension, heart insufficiency, heart arrhythmia or cephalalgia. U.S. Pat. No. 4,462,983 to Azria et al. proposes the use of certain ergot peptide alkaloids adapted for nasal or pulmonary administration.
The pharmacological actions of ergot alkaloids are varied and complex, but in general appear to result from their actions at adrenergic, dopaminergic and serotoninergic receptors. The spectrum of effects depends on the agent, dosage, species, tissue, and experimental or physiological conditions. In general, ergot alkaloids are characterized by erratic absorption and a high hepatic first pass effect with wide biotransformation. More specifically, gastrointestinal absorption of ergot alkaloids is low, due to the high hepatic first pass, and sometimes erratic. Moreover, the administration of ergot alkaloids can occasionally be associated with adverse events, particularly vascular and cardiac. Drugs, such as ergot alkaloids, that are susceptible to high hepatic clearance may need to be administered in higher doses in order to maintain blood concentrations above the minimum effective concentration for a sufficient amount of time to provide the desired pharmacological effect. However, when conventional drug delivery systems are used, the burst of drug absorption that occurs just after its administration may cause blood concentrations to exceed the minimum toxic concentration. One method of avoiding this deleterious effect is to employ lower dosage levels with more frequent dosing. Frequent dosing is not an ideal solution, however, because of the inconvenience, the increased cost and the increased likelihood that the patient will forget to take the proper number of doses. Another method of keeping drug concentration on a narrow therapeutically active level is to administer the drug using sustained-release drug delivery systems.
Sustained-release drug delivery systems include any drug delivery system that achieves slow release of the drug over an extended period of time. There are two general types of sustained-release systems: controlled-release and prolonged-release. Controlled-release systems maintain constant drug levels in the target tissue or cells. Prolonged-release systems are unable to maintain a constant drug level, but nevertheless prolong the therapeutic blood or tissue level of the drug for an extended period of time.
When designing sustained-release delivery systems many variables may be considered including the route of drug delivery, the type of delivery system, the specific properties of the drug being administered, and the bioavailability of the drug. Sustained-release delivery systems have been proposed for a number of different drugs. For example, U.S. Pat. No. 4,389,393 to Schor et al. proposes sustained release therapeutic compositions based on high molecular weight hydroxypropylmethylcellulose. U.S. Pat. No. 5,069,911 to Züger proposes a controlled release formulation for oral administration of a 9,10-dihydro ergot alkaloid, U.S. Pat. No. 5,128,142 to Mulligan et al. proposes a controlled release formulation that includes an absorbate of a mixture of a pharmaceutically useful active ingredient and an inactive substance adsorbed on a cross-link polymer.
While these references propose sustained-release delivery systems that may provide slow release of a particular drug over an extended period of time, they fail to provide such a system that also maintains or increases the bioavailability of the administered drug as compared to conventional delivery systems.